The present invention relates to a fuel injection control system for an engine of a motor vehicle having a continuously variable belt-drive transmission, and more particularly to a fuel injection system where a basic fuel injection pulse width is drived from a look-up table.
In recent years, it has been proposed that a two-cycle engine is provided with an electronically controlled fuel injector.
Japanese Utility Model Application Laid-Open 58-169117 discloses a fuel injection control system where the quantity of fuel to be injected is determined in accordance with an intake air quantity detected by an air flow meter and engine speed. In a system disclosed in Japanese Patent Application Laid-Open 63-255543, the fuel injection quantity is determined in accordance with an intake air pressure detected by a pressure sensor provided downstream of a throttle valve, and the engine speed.
Japanese Patent Application Laid-Open 63-29039 discloses a fuel injection control system where the intake air quantity is estimated based on a throttle valve opening degree detected by a throttle position sensor, and engine speed. Such a fuel injection system is relatively widely used for the engine, because the air-flow meter and the pressure sensor can be obviated. Thus, the system can be simplified and the manufacturing cost reduced. However, it is necessary to increase the basic quantity of the injected fuel when the throttle valve is rapidly opened for acceleration.
Japanese Patent Application Laid-Open 57-116138 discloses a fuel injection system wherein, whether the engine is in a steady state or a transient state is determined in dependency on a throttle valve opening speed. In the steady state, a basic fuel injection pulse width is retrieved from a look-up table storing a plurality of basic injection pulse width in accordance with the intake pressure and engine speed. When the transient state is determined, the basic fuel injection pulse width is retrieved from another look-up table storing a plurality of pulse widths, arranged in accordance with the throttle opening degree and engine speed.
However, in order to provide two tables, a memory having a large capacity must be provided. In addition, a computing process for determining the condition of the engine is complicated, resulting in increase of the capacity of the microcomputer.
Moreover, a problem occurs when the fuel injection system is applied to an engine of a motor vehicle having a continuously variable belt-drive transmission where the transmission ratio is continuously changed in accordance with engine speed and engine load. More particularly, the continuously variable transmission is connected with the crankshaft of the engine when the engine speed becomes higher than a certain speed which is substantially constant. On the other hand, in the transient state such as rapid starting of the vehicle, the throttle valve is quickly opened. However, the speed of the engine does not quickly increase. Therefore, the pulse width derived from the look-up table in accordance with the throttle opening degree and the engine speed is not wide enough to rapidly start the vehicle. In other words, the vehicle can not be rapidly accelerated.